Calcium PillsCalcium supplementation is important for bone health and strength. There are two main forms of calcium supplements: calcium citrate and calcium carbonate. These two forms differ in how they should be taken since they are absorbed differently.

Although it does not necessarily matter what time of day calcium supplements are taken, calcium carbonate is best with meals. It is also recommended that calcium supplementation be split into doses of 500 mg or less of elemental calcium per dose for best absorption. In addition, timing may be an important consideration if you take other medication that interacts with calcium, as discussed below.

Calcium Carbonate

Calcium carbonate should be taken with a meal for best absorption. It needs an acidic environment for optimal absorption and the stomach acid that is released while eating helps this process.

It is not the best form to use for calcium supplementation when on histamine-2 receptor blockers (ranitidine, famotidine) or proton pump inhibitors (omeprazole, esomeprazole, lansoprazole, pantoprazole) since these can decrease acidity in the stomach and decrease the absorption of the calcium carbonate.

Calcium carbonate is 40% elemental calcium, so 1250 mg of calcium carbonate contains 500 mg of elemental calcium.

Calcium Citrate

Calcium citrate is the other most common form of calcium supplementation. This form does not depend on an acidic environment for absorption, so it can be taken with or without food and is the best form to take when taking medications for heartburn or acid reflux.

Calcium citrate contains about 21% elemental calcium, so 950 mg of calcium citrate contains 200 mg of elemental calcium. This means taking more of this would be necessary to reach the recommended daily intake since it is less concentrated than calcium carbonate.

Recommended Daily Calcium Intake

Recommended daily calcium intake for bone health is listed in the table below.

0-6 months
200 mg
200 mg
7-12 months
260 mg
260 mg
1-3 years
700 mg
700 mg
4-8 years
1000 mg
1000 mg
9-13 years
1300 mg
1300 mg
14-18 years
1300 mg
1300 mg
19-50 years
1000 mg
1000 mg
51-70 years
1000 mg
1200 mg
71 years and older
1200 mg
1200 mg

Side Effects

Side effects are not commonly experienced, but can include:

  • Gas
  • Bloating
  • Constipation

Too much calcium in the body may cause kidney problems, kidney stones, and other calcifications.


Calcium may interact with other medications and should be discussed with a healthcare provider. Some drugs calcium may interact with are:

  • Iron supplements
  • Bisphosphonates (alendronate, risedronate, zoledronic acid)
  • Fluoroquinolone antibiotics (moxifloxacin, levofloxacin, ciprofloxacin)
  • Tetracycline antibiotics (doxycycline, minocycline, tetracycline)
  • Levothyroxine
  • Phenytoin

Dietary Sources

It is also important to try and eat a balanced diet and get calcium from foods, if possible. Foods that contain calcium are:

  • Vegetables (cabbage, kale, broccoli)
  • Dairy (yogurt, milk, cheese, creams)
  • Certain cereals


  • Inform your healthcare provider(s) when taking calcium supplementation
  • Before starting calcium supplementation or a new medication, check with a healthcare provider or pharmacist to ensure they do not interact
  • Inform a healthcare provider if you experience severe constipation